A conventionally known type of entrapment detecting device is provided with a Hall IC (i.e. a rotation detecting sensor) for detecting variation of magnetic force of a magnet provided on a rotary shaft of a motor, thereby determining whether or not an object or an obstacle has been entrapped. More particularly, in the entrapment detecting device, the entrapment determination is performed by detecting a position of the magnet based upon the counted number of edges of a pulse signal outputted from the rotation detecting sensor, by calculating a rotational speed of the motor based upon cycles of the pulse signal, and by obtaining how much the rotational speed of the motor was decreased.
When an opening/closing member, such as a sunroof, or a power window, operates for opening or closing an open area, no constant load is applied to the opening/closing member within the open area. For example, there has been a sunroof apparatus for a vehicle, which is provided with a wind deflector (hereinafter, referred to as a deflector) for restraining hissing or pulsating wind sound which may occur while the vehicle is running with a roof opened. When the sunroof (i.e. the opening/closing member) operates for closing the open area, the sunroof is required to tilt down arm portions of the deflector so as to house the deflector in the vehicle roof. The deflector generally upstands being applied with reaction force of a spring. Therefore, the load applied to the opening/closing member upon tilting down the deflector is greater than load applied to the opening/closing member within a range in which the deflector is not required to be tilted down (hereinafter, referred to as a normal range), wherein load applied to the motor is increased and the motor rotational speed is hence decreased.
In the above-disclosed sunroof apparatus for a vehicle, it may not be accurately judged whether the decrease of the motor rotational speed has occurred due to the tilting-down operation of the deflector by the opening/closing member or due to the entrapment of the object or the obstacle between the opening/closing member and the fixed member. Therefore, a judging unit of the sunroof apparatus may judge that the entrapment has occurred when the deflector is tilted down by the opening/closing member with no entrapment therebetween. In such a case, the movement of the opening/closing member to close the open area may be erroneously stopped and the opening/closing member may be further erroneously moved in a reverse direction for opening the open area.
In order to prevent the above-described erroneous operation of the opening/closing member due to the misjudgment of the entrapment, recent developments have lead to an entrapment detecting device, in which a predetermined operational area, in which the motor rotational speed is changed based upon slidable movement of the opening/closing member, is divided into plural ranges, and a threshold value for determining the occurrence of the entrapment is preset in each range. The threshold value is denoted with the rotational speed. The judging unit of the entrapment detecting device determines the occurrence of the entrapment when the decreasing amount of the motor rotational speed per unit of time becomes greater than the threshold value. One of the plural ranges of the operational area is a range in which the deflector is tilted down by the sunroof. The threshold value in this range is preset at a relatively high value, i.e. at a relatively great decreasing amount of the motor rotational speed so as to prevent the misjudgment of the entrapment. In this case, when the motor rotational speed is decreased with no entrapment, the decreasing amount of the motor rotational speed does not exceed the threshold value, thereby capable of preventing the misjudgment of the entrapment, i.e. capable of preventing the erroneous operation of the opening/closing member.
Further, sliding resistance of the sunroof may vary due to fluctuation of the motor rotational speed due to temperature change, aging distortion of the sunroof, or the like. The threshold value for detecting the occurrence of the entrapment is required to be preset at a relatively high value considering various factors of the fluctuation of the motor rotational speed. Still further, pushed-down portions of the deflectors may be assembled with individual differences. The plural ranges with the relatively highly preset threshold value are preferably required to cross widely over the operational area to a certain degree. In such a case, considering the ranges in which the deflector is not tilted down by the opening/closing member and the motor rotational speed is not decreased, the threshold value in these ranges may be set at a relatively high value. Therefore, when the entrapment occurs without tilting-down the deflector in these ranges, the load applied to the object or the obstacle may become greater than the load applied to the object or the obstacle within the normal range. This may lead to damage on the object or the obstacle.
The above-described problem occurs due to the fluctuation of the load applied to the opening/closing member when the opening/closing member is moved for closing the operational area with no entrapment between the opening/closing member and the fixed member. Therefore, the present invention seeks to provide an improved entrapment detecting device for an opening/closing member capable of detecting entrapment independently of the fluctuation of the load applied to the opening/closing member when the opening/closing member is moved for closing the operational area with no entrapment between the opening/closing member and the fixed member.